There are plenty of sites out there. You can pull up a good ten of them just by typing it into Google. I personally go through 4wheelpartsonline.com. I bought a 2010 last year and ran the 4" Aries running boards. They bolted right up in about 10 minutes. There's also a sticky at the top of the parts/accessories forum that'll give you a good starting point as well.
cant go wrong with autoanything.com... free shipping and big discounts most of the time. i just got the go rhino dominator II's in stainless and i love em. they fit tight to the body of the truck and look awesome. they have dozens of different styles and brands so try there before you make a move